The present invention relates to a superconducting wire or a superconductor formed by combining an oxide superconducting substance that exhibits superconductivity when cooled to the freezing point of 63 K of liquid nitrogen and a metallic body with controlled crystal orientation, and capable of carrying currents in a high superconducting critical current density (Jc) in a magnetic field, and a method of manufacturing the same.
The present invention relates also to superconducting magnets, superconducting NMR apparatuses, superconducting MRI apparatuses, superconducting generators, superconducting energy storage devices, magnetic shielding devices, synchrotron radiation generators, magnetic separators and elementary particle accelerators employing the aforesaid superconducting wire or the superconductor and having economic advantages far greater than those of the conventional ones.
The present invention relates also to a silver tape having a cubic aggregate structure invented during the course of the development of a superconducting wire or a superconductor capable of carrying current in a high Jc, and a method of manufacturing the same.
Tens of oxide superconducting substances have been discovered since the first high-temperature oxide superconducting substance was discovered in 1986. Studies of the oxide superconducting substances of the following four systems, among those hitherto discovered, are being currently made for the practical application thereof owing to their stability and ease of composition. EQU (Tl.sub.1-X1-X2 Pb.sub.X1 Bi.sub.X2)(Sr.sub.1-X3 Ba.sub.X3).sub.2 Ca.sub.n-1 Cu.sub.n O.sub.2n+3 (1)
where:
0.ltoreq.X1.ltoreq.0.9 PA1 0.ltoreq.X2.ltoreq.0.5 PA1 0.ltoreq.X1+X2.ltoreq.1 PA1 0.ltoreq.X3.ltoreq.1 PA1 n=1, 2, 3, 4 or 5 PA1 n=1, 2, 3, 4 or 5 PA1 0.ltoreq.X1.ltoreq.0.4 PA1 n=1, 2 or 3 PA1 Ln is Y or a rare earth element PA1 -0.5.ltoreq.X1.ltoreq.0.1 PA1 (Tl.sub.X1 Pb.sub.X2 Bi.sub.X3 Hg.sub.X4 Cu.sub.X5)(Sr.sub.1-X6 Ba.sub.X6).sub.2 Ca.sub.n-1 Cu.sub.n O.sub.2n+3+X7 ; where 0.ltoreq.X1.ltoreq.1.0, 0.ltoreq.X2.ltoreq.1.0, 0.ltoreq.X3.ltoreq.0.5, 0.ltoreq.X4.ltoreq.1.0, 0.ltoreq.X5.ltoreq.1.0, 0.5.ltoreq.X1+X2+X3+X4+X5.ltoreq.1, 0.ltoreq.X6.ltoreq.1, -0.5.ltoreq.X7.ltoreq.0.5, and n=1, 2, 3, 4 or 5. Oxide superconducting substances having compositions represented by LnBa.sub.2 Cu.sub.3 O.sub.7+X1, where Ln is Y or a rare earth element, and -0.5.ltoreq.X1.ltoreq.0.1, have each a high irreversible magnetic field and are preferable oxide superconducting substances. Although superconducting substances having compositions represented by (Tl.sub.1-X1-X2-X3 Pb.sub.X1 Bi.sub.X2 Hg.sub.X3) .sub.2 (Sr.sub.1-X4 Ba.sub.X4).sub.2 Ca.sub.n-1 Cu.sub.n O.sub.2n+3+X5, where n=2, 3, 4, 5, or 6, 0.ltoreq.X1.ltoreq.0.8, 0.ltoreq.X2.ltoreq.0.5, 0.ltoreq.X3.ltoreq.1.0, 0.ltoreq.X1+X2+X3.ltoreq.1, 0.ltoreq.X4.ltoreq.1, and -0.5.ltoreq.X5.ltoreq.0.5, have comparatively small irreversible magnetic fields as compared with those of the superconducting substances of the Tl-1-layer system or the Y system, these substances may be used.
(these oxide superconducting substances will be designated as those of the Tl-1-layer system).
Tl.sub.2 Ba.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.2n+4 (2)
where:
(these oxide superconducting substances will be designated as those of the Tl-2-layer system). EQU (Bi.sub.1-X1 Pb.sub.X1).sub.2 Sr.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.2n+4 (3)
where:
(these oxide superconducting substances will be designated as those of the Bi-2-layer system). EQU LnBa.sub.2 Cu.sub.3 O.sub.7+X1 (4)
where:
(these oxide superconducting substances will be designated as those of the Y system).
The substances of the Bi-2-layer system have crystals that can be easily oriented, have crystal boundaries that carry superconductive current smoothly and, therefore, are capable of carrying currents in a high superconductive transport current density (transport Jc) when any magnetic field is not applied thereto ("Japanese Journal of Applied Physics", Vol. 30, pp. L2083-L2084, 1991). The substances of the Bi-2-layer system have, owing to their intrinsic crystal structures, a fatal problem that their pinning forces are very weak at temperatures to which the substances can be cooled in liquid nitrogen ("Physica C", Vol. 177, pp. 431-437, 1991). Therefore, the substances of the Bi-2-layer system are suitable for forming superconducting wires having excellent characteristics to be used at temperatures below about 40 K, however, those substances could not have been used for forming superconducting wires to be used at temperatures of 60 K or above.
The substances of the Tl-1-layer system and the Tl-2-layer system maintain high pinning force at temperatures up to temperatures near their critical temperatures, however, their crystals are difficult to be oriented. Therefore, the crystal boundaries of those substances do not pass superconducting current smoothly, and superconducting wires of those substances having transport Jc exceeding 10,000 A/cm.sup.2 in a magnetic field of 1 T at 77 K, which is regarded as a standard for practical application, have not been obtained ("Physica C", Vol. 220, pp. 310-322, 1994; "Hitachi Review", Vol. 39, p. 55, 1990; "Japanese Journal of Applied Physics", Vol. 27, pp. L185-L187, 1988).
Recently, many laboratories have made studies to obtain superconducting wires capable of carrying currents in a high Jc at 77 K in a magnetic field by orienting the crystals of substances of the Tl-1-layer system and the Y system that exert high pinning forces at 77 K. For example, Iijima, et al. published a method of making a superconducting substance of the Y system in "Proceedings of 5th International Symposium on Superconductivity", Nov. 16-19, 1992, Kobe, Japan, pp. 661-664. This method forms an yttria-stabilized zirconia layer of oriented crystals on a polycrystalline Ni-base alloy substrate by an Ion-beam-assisted deposition process, and then makes a superconducting substance of the Y system on the yttria-stabilized zirconia layer by a pulsed laser deposition process. Deluca, et al. published a method of making a superconducting substance of the Tl-1-layer system on a polycrystalline yttria-stabilized zirconia by spray pyrolysis in "Physica C", Vol. 205, pp. 21-31, 1993. Yoshino, et al. disclosed a method of manufacturing a superconductor of oriented crystals, using a silver tape of crystals having faces (1 0 0) or (1 1 0) aligned in parallel to the rolled surface in Japanese Patent Laid-open (Kokai) No. 3-9311. Yoshino, et al. published a method of making a superconducting substance of the Y system on a silver tape of silver crystals having faces (1 1 0) aligned in parallel to the surface of the silver tape by an ionized cluster beam deposition process in "Abstracts of 6th International Symposium on Superconductivity", Oct. 26-23, 1992, Hiroshima, Japan, p. 119.
So far, superconducting wires having practically acceptable performance characteristics at temperatures of or above the temperature to which the superconducting wires can be cooled in liquid nitrogen could not have been manufactured and there have been no superconducting apparatus capable of operation when cooled with a refrigerant having a boiling point higher than that of liquid helium, such as liquid nitrogen.
So far, any silver tapes of a cubic aggregate structure in which the faces {1 0 0} of the crystals are aligned with the orientations &lt;1 0 0&gt; have not been obtained (S. Nagashima, "Shyugo Soshiki", Maruzen)